There are two different types of network nodes in a network deployment scenario, which are evolved base stations (Evolved NodeB, eNB) and small cell nodes (Small Cell Node, SCN). An eNB and an SCN separately control one or more cells, and a cell under the eNB and a cell under the SCN may use different frequencies. The cell under the eNB covers a larger area, and may be referred to as a macro cell; the cell under the SCN covers a smaller area, and may be referred to as a small cell.
In the prior art, any one of the following situations may occur:
a time alignment timer (Time Alignment Timer, TAT) set for a macro cell in a user equipment (User Equipment, UE) expires, and the UE needs to send uplink data or signaling to an eNB;
a UE does not have a resource for sending a scheduling request (Scheduling Request, SR) on a macro cell, and the UE needs to send uplink data or signaling to an eNB; and
a UE fails to send a dynamic scheduling request (Dynamic Scheduling Request, DSR) on the macro cell, where the DSR failure refers to that a quantity of times that the UE continuously sends an SR exceeds a preset maximum quantity of times.
When any one of the foregoing three situations occurs, the UE needs to first initiate a contention-based random access procedure to the eNB, and only after this procedure is completed, the UE can send the uplink data or signaling to the eNB, and then the eNB may send, to the UE, downlink data or signaling in response to the uplink data or signaling. The contention-based random access procedure is defined in detail in the 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) protocol TS 36.321.
The inventors of the present invention find that, the contention-based random access procedure used in the prior art is complex, and has a very long access delay.